In the coming year our program will continue in four areas. Our major emphasis will be on studies in iron metabolism with attention to the mechanism of absorption, of exchange of iron between cells. Specific studies will be directed at identification of iron loading individuals and in the use of ferritin to evaluate body iron stores. Oxygen transport and work performance will be examined with particular reference to the respective role of variations in blood volume and hemoglobin concentration on work performance on the one hand and variations in muscle function on the other. Erythrocyte studies include the use of cyanate as a red cell tag, the use of indium in delineating the red cell marrow, studies into the nature of the storage lesion which occurs when the red cell is maintained in vitro, and the effect of oxygen inhalation on erythropoiesis in sickle cell disease. Granulocyte studies will be concerned with white cell procurement and preservation and on granulocyte kinetics in clinical disorders. BIBLIOGRAPHIC REFERENCES: Finch, C. A. Erythropoiesis in protein-calorie malnutrition. In Protein-Calorie Malnutrition (The Nutrition Foundation), ed. R. E. Olson. Academic Press, 1975, pp. 247-256. Lipschitz, D. A., J. D. Cook, and C. A. Finch. Ferritin in formed blood elements. Proc. Soc. Exp. Biol. Med. 148:358-364, 1975.